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Autres articles (22)
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Librairies et logiciels spécifiques aux médias
10 décembre 2010, parPour un fonctionnement correct et optimal, plusieurs choses sont à prendre en considération.
Il est important, après avoir installé apache2, mysql et php5, d’installer d’autres logiciels nécessaires dont les installations sont décrites dans les liens afférants. Un ensemble de librairies multimedias (x264, libtheora, libvpx) utilisées pour l’encodage et le décodage des vidéos et sons afin de supporter le plus grand nombre de fichiers possibles. Cf. : ce tutoriel ; FFMpeg avec le maximum de décodeurs et (...) -
Other interesting software
13 avril 2011, parWe don’t claim to be the only ones doing what we do ... and especially not to assert claims to be the best either ... What we do, we just try to do it well and getting better ...
The following list represents softwares that tend to be more or less as MediaSPIP or that MediaSPIP tries more or less to do the same, whatever ...
We don’t know them, we didn’t try them, but you can take a peek.
Videopress
Website : http://videopress.com/
License : GNU/GPL v2
Source code : (...) -
Gestion générale des documents
13 mai 2011, parMédiaSPIP ne modifie jamais le document original mis en ligne.
Pour chaque document mis en ligne il effectue deux opérations successives : la création d’une version supplémentaire qui peut être facilement consultée en ligne tout en laissant l’original téléchargeable dans le cas où le document original ne peut être lu dans un navigateur Internet ; la récupération des métadonnées du document original pour illustrer textuellement le fichier ;
Les tableaux ci-dessous expliquent ce que peut faire MédiaSPIP (...)
Sur d’autres sites (6118)
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Playing RTSP in WPF application with low latency using FFMPEG / FFMediaElement (FFME)
22 mars 2019, par PabokaI’m trying to use FFMediaElement (FFME, WPF MediaElement replacement based on FFmpeg) component to play RSTP live video in my WPF application.
I have a good connection to my camera and I want to play it with minimum available latency.
I’ve reduced the latency by changing
ProbeSizeto its minimal value :private void Media_OnMediaInitializing(object Sender, MediaInitializingRoutedEventArgs e)
{
e.Configuration.GlobalOptions.ProbeSize = 32;
}But I still have about 1 second of latency since the very beginning of the stream. I mean, when I start playing, I have to wait for 1 second till the video appears and then I have 1s of latency.
I’ve also tried to change following parameters :
e.Configuration.GlobalOptions.EnableReducedBuffering = true;
e.Configuration.GlobalOptions.FlagNoBuffer = true;
e.Configuration.GlobalOptions.MaxAnalyzeDuration = TimeSpan.Zero;but it gave no result.
I measured time-interval between FFmpeg output lines (the number in the first column is the time, elapsed from the previous line, ms)
---- OpenCommand: Entered
39 FFInterop.Initialize: FFmpeg v4.0
0 EVENT START: MediaInitializing
0 EVENT DONE : MediaInitializing
379 EVENT START: MediaOpening
0 EVENT DONE : MediaOpening
0 COMP VIDEO: Start Offset: 0,000; Duration: N/A
41 SYNC-BUFFER: Started.
609 SYNC-BUFFER: Finished. Clock set to 1534932751,634
0 EVENT START: MediaOpened
0 EVENT DONE : MediaOpened
0 EVENT START: BufferingStarted
0 EVENT DONE : BufferingStarted
0 OpenCommand: Completed
0 V BLK: 1534932751,634 | CLK: 1534932751,634 | DFT: 0 | IX: 0 | PQ: 0,0k | TQ: 0,0k
0 Command Queue (1 commands): Before ProcessNext
0 Play - ID: 404 Canceled: False; Completed: False; Status: WaitingForActivation; State:
94 V BLK: 1534932751,675 | CLK: 1534932751,699 | DFT: 24 | IX: 1 | PQ: 0,0k | TQ: 0,0kSo, the most the process of "sync-buffering" takes the most of the time.
Is there any parameter of FFmpeg which allows reducing a size of the buffer ?
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How to extract motion vectors from h264 without a full decode on the CPU
25 septembre 2020, par Adrian MayI'm trying to use my nose as a pointing device. The plan is to encode the video stream from a webcam pointed at my face as h264 or the like, get the motion vectors, cook the numbers a bit and chuck them into /dev/uinput to make the mouse pointer move about. The uinput bit was easy.


This has to work with zero discernable latency. This, for instance :


#!/bin/bash
[ -p pipe.mkv ] || mkfifo pipe.mkv
ffmpeg -y -rtbufsize 1M -s 640x360 -vcodec mjpeg -i /dev/video0 -c h264_nvenc pipe.mkv &
ffplay -flags2 +export_mvs -vf codecview=mv=pf+bf+bb pipe.mkv


shows that the vectors are there but with a latency of several seconds which is unusable in a mouse. I know that the first ffmpeg step is working very fast by using the GPU, so either the pipe or the h264 decode in the second step is introducing the latency.


I tried MV Tractus (same as mpegflow I think) in a similar pipe arrangement and it was also very slow. They do a full h264 decode on the CPU and I think that's the problem cos I can see them imposing a lot of load on one CPU. If the pipe had caused the delay by buffering badly then the CPU wouldn't have been loaded. I guess ffplay also did the decoding on the CPU and I couldn't persuade it not to, but it only wants to draw arrows which are no use to me.


I think there are several approaches, and I'd like advice on which would be best, or if there's something even better I don't know about. I could :


- 

- Decode in hardware and get the motion vectors. So far this has failed. I tried combining ffmpeg's
extract_mvs.candhw_decode.csamples but no motion vectors turn up. vdpau is the only decoder I got working on my linux box. I have a nvidia gpu. - Do a minimal parse of the h264 to fish out the motion vectors only, ignoring all the other data. I think this would mean putting some kind of "motion only" option in libav's parser, but I'm not at all familiar with that code.
- Find some other h264 parsing library that has said option and also unpacks the container.
- Forget about hardware accelerated encoding and use a stripped down encoder to make only the motion vectors on either CPU or GPU. I suspect this would be slow cos I think calculating the motion vectors is the hardest part of the algorithm.










I'm tending towards the second option but I need some help figuring out where in the libav code to do it.


- Decode in hardware and get the motion vectors. So far this has failed. I tried combining ffmpeg's
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Extracting frames from a video does not work correctly [closed]
13 avril 2024, par Al TilmidhUsing the libraries (libav) and (ffmpeg), I try to extract frames as
.jpgfiles from avideo.mp4, the problem is that my program crashes when I use theCV_8UC3parameter, but by changing this parameter toCV_8UC1, the extracted images end up without color (grayscale), I don't really know what I missed, here is a minimal code to reproduce the two situations :

#include <opencv2></opencv2>opencv.hpp>

extern "C"
{
#include <libavformat></libavformat>avformat.h>
#include <libavcodec></libavcodec>avcodec.h>
}

int main()
{
 AVFormatContext *formatContext = nullptr;

 if (avformat_open_input(&formatContext, "video.mp4", nullptr, nullptr) != 0)
 {
 return -1;
 }

 if (avformat_find_stream_info(formatContext, nullptr) < 0)
 {
 return -1;
 }

 AVPacket packet;
 const AVCodec *codec = nullptr;
 AVCodecContext *codecContext = nullptr;

 int videoStreamIndex = av_find_best_stream(formatContext, AVMEDIA_TYPE_VIDEO, -1, -1, &codec, 0);
 if (videoStreamIndex < 0)
 {
 return -1;
 }

 codecContext = avcodec_alloc_context3(codec);
 avcodec_parameters_to_context(codecContext, formatContext->streams[videoStreamIndex]->codecpar);

 if (avcodec_open2(codecContext, codec, nullptr) < 0)
 {
 return -1;
 }

 AVFrame *frame = av_frame_alloc();

 while (av_read_frame(formatContext, &packet) >= 0)
 {
 if (packet.stream_index == videoStreamIndex)
 {
 int response = avcodec_send_packet(codecContext, &packet);
 
 if (response < 0)
 {
 break;
 }

 while (response >= 0)
 {
 response = avcodec_receive_frame(codecContext, frame);
 if (response == AVERROR(EAGAIN))
 {
 // NO FRAMES
 break;
 }

 else if (response == AVERROR_EOF)
 {
 // END OF FILE
 break;
 }

 else if (response < 0)
 {
 break;
 }

 //cv::Mat frameMat(frame->height, frame->width, CV_8UC3, frame->data[0]); // CV_8UC3 → THE PROGRAM CRASHES
 cv::Mat frameMat(frame->height, frame->width, CV_8UC1, frame->data[0]); // CV_8UC1 → WORK BUT IMAGES ARE IN GRAYSCALE
 cv::imwrite("frame_" + std::to_string(frame->pts) + ".jpg", frameMat);
 }
 }

 av_packet_unref(&packet);
 }

 av_frame_free(&frame);
 avcodec_free_context(&codecContext);
 avformat_close_input(&formatContext);

 return 0;
}


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